Powdered fire extinguishing agents

ABSTRACT

Powdered fire-extinguishing agents based on ammonium phosphates and substantially containing ammonium polyphosphates with a degree of condensation higher than 50.

Elite States Patent [191 Briill et a1.

Assignee: Knapsack Aktiengesellschaft,

Knapsack near Cologne, Germany Filed: Nov. 17, 1971 Appl. N0.: 199,761

Related US. Application Data Continuation of Ser. No. 830,127, June 3, 1969,

abandoned.

Foreign Application Priority Data June 3, 1969 Germany P 17 71 540.1

US. Cl 252/7, 252/2, 252/5, 423/305 51 Aug. 28, 1973 [51] int. Cl A62d 1/00 [58] Field of Search 252/2, 5, 7; 23/106 A, 106 R [56] References Cited UNITED STATES PATENTS 3,397,035 8/1968 Shen et al. 23/106 3,495,937 2/1970 Shen et a1. 23/106 3,333,921 8/1967 Knollmueller 2.3/106 Primary Examiner-George F; Lesmes Assistant Examiner-William R. Dixon, Jr.

A t tofiiy Arthur G. Connolly, Albert P. Bower et a1.

1 Claim, No Drawings POWDERED FIRE EXTINGUISHING AGENTS This application is a continuation of application Ser. No. 830,127, filed June 3, 1969, now abandoned.

The present invention relates to powdered fireextinguishing agents containing phosphates as their active fire-extinguishing component.

Powdered fire-extinguishers are gaining increasing interest for use in fighting fire outbreaks occasioned'by liquids or tires, or fire outbreaks in electrical installations. The reason for this is more particularly that they often make the flames extinguish instantaneously, which is very advantageous. Still further, powdered fire-extinguishers of suitable composition produce on the ignited object a cover, which effectively prevents extinguished fire from: being revived, for example, by reignition caused by hot metal parts or glow residues.

Conventional dry. fire-extinguishing powders often contain sodiumbicarbonate as their principal constituent which has certain additives therein to render ithydrophobic and flowable.

The fire-extinguishing powders which have more recently been used consist substantially of phosphates, which are more particularlyprimary or secondary ammonium phosphates, andhave the distinctionofcombining very good fire-extinguishing effects with'a very good covering power. However, the weight of these powders restricts their use in aircraft fire-extinguisher appliances or in fire-vehicles.

It has now been found that substantially less great quantities of fire-extinguisher are needed, using dry, powdered fire-extinguishers consisting wholly or substantially of ammonium-polyphosphates with a degree of condensation of more than 50.

Especially good results are obtained with the use of ammonium polyphosphates having a degree of condensation between 200 and 500, preferably between 300 and 400.

The ammonium polyphosphates suggested to be used in accordance with the present invention have .an apparent density between about 0.4 and 0.9 kg/liter. As compared with conventional powdered fireextinguishers, it has been found that very substantial weight economies can be effected for an equally good fire-extinguishing power, using ammonium polyphosphates having the above degree of condensation and an apparent density between about 0.4 and 0.45 kg/liter.

The above ammonium polyphosphates can be produced from polyphosphoric acid containing more than 76 weight percent P 0 preferably between 82 and 86 weight percent P 0 To this effect, the acid is heated to temperatures between 8 and 100C and gaseous ammonia is introduced without any supply of further heat. The heat of neutralization set free produces a temperature increase in the reaction mixture, which is maintained, if desired by cooling, between 300 and 330C, preferably 310 and 320C, until thetemperature itself commences to fall below 300C. The reaction mixture is then allowed to stand, if necessary while supplying further heat, at temperatures between 230 and 270C, preferably between 245 and 255C, until formation of a viscous crystalline magma which practically ceases to absorb further ammonia. The resulting reaction product is then cooled, washed with cold water and dried at temperatures lower than 100C.

When it is desired to produce ammonium polyphosphates with an average chain length n between 20 and 90, then the isolated reaction product is annealed for a period'of at least 15 minutes at to 320C in a gaseous ammonia atmosphere having between 1 and 5 percent by volume steam therein.

Products with a mean chain length n between 100 and 400are obtained by annealing the isolated reaction product for a period of at least 15 minutes, at temperatures between 220 and 320C in apure ammonia atmosphere.

The degree of condensationis determined by the J .R. VanWazer-method reported in Analytical Chemistry 26' (1954), pages 1755-59, after dissolution of the product in hot water.

The novel fire-extinguishing powders are rendered hydrophobic and flowable in conventional manner, for example, by theadditionof small amounts of polysiloxanes or magnesium stearate, and are foam-compatible.

The following Examples illustrate the advantageous properties of the novel fire-extinguishing powders.

EXAMPLE 1 A trough with a cross-sectional area of 1 square meter and 12 cmhigh was filled first with 5 liters water for levelling purposes, and 25 liters Diesel oil were poured thereonto. The Diesel oil was ignited, allowed to burn for 5 minutes and extinguished. The extinguisher was ammonium polyphosphate with a degree of condensation between 300 and 400 and an apparent density of about 0.4 kg/liter. Comparative tests were carried out using commercial dry fire-extinguishing powders, so-called ABC- and BCE-powders. ABC- powder is a mixture which substantially consists of primary and secondary ammonium phosphates and sodium bicarbonate; it is used for extinguishing fire outbreaks as defined by fire classes A, B and C. BCE- powder consistsof sodium bicarbonate and is used for extinguishing fire outbreaks as defined by fire clases B, C and E. (Fire class A combustible, solid organic materials; fire class B combustible liquids, fire class C combustible gases, fire class E electrical installations). The following average quantities of fireextinguisher were needed in a series of tests.

Ammonium polyphosphate 1100 grams ABC-powder 2050 grams BCE-powder 2150 grams EXAMPLE 2 Troughs similar to those used in Example 1 were filled first with water for levelling purposes and then with 25litersgasoline. The gasoline was ignited, al-

lowed to burn for 60 seconds and extinguished. The fire-extinguishers used comprised those specified in Example l and ammonium polyphosphate with a conden sation degree of about 100 and an apparent density of 0.8 kg/liter. The following quantities of fireextinguishers were needed:

Ammonium polyphosphate; degree of condensation between 300 and 400; 1500 grams apparent density 0.4 kg/liter Ammonium polyphosphate, degree of condensation 100; apparent 2200 grams density 0.8 kg/liter ABC-powder 3000 grams BCE-powder 2400 grams EXAMPLE 3 25 liters of a polar solvent-mixture placed in troughs similar to those used in the preceding Examples were ignited, allowed to burn for 2 minutes and extinguished. The following average quantities of fireextinguisher were needed:

Ammonium polyphosphate; degree of EXAMPLE 4 Gasoline was poured over automobile tires identical as to origin and dimensions, which were ignited, allowed to burn for 4 minutes and extinguished. The following average quantities of extinguisher were needed: Ammonium polyphosphate; degree of condensation between 300 and 400; 200 grams apparent density 04 kg/liter Ammonium polyphosphate; degree of condensation I; apparent density 350 grams 0.8 kg/liter ABC-powder 550 grams,

EXAMPLE 5 Foam compatibility Ammonium polyphosphate (degree of condensation between 300 and 400; apparent density: 0.4 kg/liter) and a commercial, officially admitted, foamcompatible powder were compared.

A round trough 20 cm wide, cm high and subdivided into two halves was used. A baby comete tube with a pouring elbow was used to introduce a commercial foam extinguisher thereinto. 8 Grams of a commercial fire-extinguishing powder were dusted onto the material in the first half of the trough and 8 grams powdered ammonium polyphosphate were dusted onto the material in the second trough half. The reduction of the foam layer height and the water separation under incident heat were observed. After 6 minutes, the commercial powder and the ammonium polyphosphate were found to have separated 96 and 98 milliliters water, respectively.

EXAMPLE 6 Foam compatibility Resistance to burning off A burn-off test was made using foam with powder dusted thereon, which was'subjected to the attack of burning gasoline. A trough with the dimensions of 400 X 900 mm and subdivided at its longitudinal side into a 3 and a section by means ofa slide plate, was filled with 10 liters gasoline, and the section was filled with foam. Excessive foam was stripped off. 150 grams of commercial powder were dusted onto the material in the trough in a first test. 100 grams ammonium polyphosphate were dusted thereonto in a second test, and 150 grams ammonium polyphosphate were used in a third test. The uncovered gasoline was allowed to burn for 20 seconds; The slide plate separating the gasoline from the foam was removed and the time needed for complete destruction of the foam layer was determined. About 9.5 minutes were needed in all three cases. A 15 min. destruction time was needed in a blank test, using merely foam.

We claim:

1. A fire extinguishing agent for use on Class A, B and C fires in powdered form, consisting essentially of ammonium polyphosphate, the latter being prepared by:

heating polyphosphoric acid containing more than 76 percent by weight P 0 to a temperature between 80C. and C,

introducing gaseous ammonia thereinto without supplying further heat; allowing the temperature in the reaction mixture to increase under the action of the liberated heat of neutralization; maintaining the reaction mixture, if necessary by cooling, between 300C. and 330C. until the temperature itself commences to fall below 300C.,

allowing the reaction mixture to stand at temperatures between 230C. and 270C. which are maintained, if necessary by supplying further heat, until formation of a viscous crystalline magma which practically ceases to absorb further ammonia;

cooling the resulting reaction product, washing it with cold water, and drying it at temperatures lower than 100C; and

annealing the dried product for a period of at least 15 minutes at temperatures between 220 and 320C. in a pure ammonia atmosphere, the said ammonium polyphosphate having an apparent density of between 0.4 and 0.45 kg/l and a degree of condensation higher than 300.

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